1. Field of the Invention
The invention relates to an automatic plug-inserting apparatus for automatically inserting a plug in a metal pipe such as an aluminum pipe which is to be drawn and elongated in a pipe-drawing equipment such as a drawbench.
2. Description of Prior Art
The drawing process as one of the processes adapted to draw and elongate aluminum pipes or aluminum-base alloy pipes has been employed particularly in a case in which wanted are ideally straight drawn pipes with a sufficiently uniform thickness of pipe walls. In a further case wherein an especially high precision is required, the so-called plug-drawing method has been adopted by which a plug is inserted in a raw pipe to be drawn.
The plug is attached to an end of a plug-supporting rod so as to be inserted at first in the raw pipe before the plug-drawing method is carried out. The plug is thus positioned inside an opening of a drawing die, and a pointed end which has previously been formed to be of a reduced diameter at an end of the raw pipe is then gripped with a chuck secured to a carriage which is driven by chains. Subsequently, the pointed end is forcibly pulled through the opening of said die so that the raw pipe is drawn to obtain its elongated shape.
Therefore, plug-inserting apparatuses are known and they have generally been used to automatically insert the plug prior to performance of the drawing method described above.
FIG. 4 illustrates one of the known plug-inserting apparatuses wherein the plug 84 is attached to a leading end of the plug-supporting rod 81 which is held at its trailing end by a support block 86 in such a state as forming a cantilever mechanism. A bottom of a portion near the leading end rests on a support roller 85 which keeps horizontal the plug-supporting rod 81. On the other hand, a pusher 83 is disposed opposite to the leading end of said plug-supporting rod so that the raw pipe 82 to be drawn can be set between the pusher 83 and the plug 84 in alignment with their axes. The raw pipe 82 is then pushed by the pusher 83 towards the plug 81, which is to be inserted in the pipe in this manner.
However, such a known plug-inserting apparatus is likely to cause scratches on surfaces of the drawn pipes, and thus inadequate for some cases wherein photosensitive base drums are manufactured to which photoconductive selenium or other organic photosensitive substances are to be applied. The photosensitive base drums must be provided with as high surface quality as possible for use in the electronic copiers or laser printers.
An outer surface of the raw pipe 82 pushed by the pusher 83 is usually scratched by a bed surface 87 on which said pipe is dragged. Further, after a leading end of the raw pipe 82 has gone beyond the support roller 85, the outer surface of said pipe itself comes into direct contact with the support roller 85, this contact also causing scratches on the outer surface of the raw pipe 82.
In addition, an axis of the raw pipe 82 cannot be aligned with an axis of the plug-supporting rod 81 any more also after said leading end of the pipe 82 has advanced ahead past the support roller 85 as shown in FIG. 5. Consequently, the plug 84 may be forced into the pipe and be early abraded thereby to shorten the life of said plug.